Structural repair of gas turbine or other superalloy components is commonly recognized as replacing damaged material with matching alloy material and achieving properties, such as strength, that are close to the original manufacture component specifications (e.g., at least seventy percent ultimate tensile strength of the original specification). For example, it is preferable to perform structural repairs on turbine blades that have experienced surface cracks, so that risk of further cracking is reduced, and the blades are restored to original material structural and dimensional specifications. These blades and vanes for land-based power generation and for aerospace applications are typically formed from superalloy materials. The term “superalloy” is used herein as it is commonly used in the art to refer to a highly corrosion-resistant and oxidation-resistant alloy that exhibits excellent mechanical strength and resistance to creep even at high temperatures. Superalloys typically include a high nickel or cobalt content.
Since the development of superalloy materials, various strategies have been employed to provide mechanical strength to the materials to improve the lifetimes thereof during new manufacture or repair. Some elements can provide strength in solid solution. Examples include Co, Cr, Fe, Mo, W, Ta, and Re. Carbide precipitations can also add to strength. Elements forming carbides include W, Ta, Ti, Mo, Nb, Hf and Cr. Most particularly, superalloy materials may be strengthened through the formation of a precipitate phase known as gamma prime. This phase has the basic composition Ni3(Al,Ti). If properly sized and of sufficient volume fraction, this phase offers significant strengthening—most particularly to nickel based superalloys. Some superalloys are also strengthened by another precipitate known as gamma double prime. This precipitate is of the composition Ni3Nb, and is important for strengthening some nickel and nickel/iron-based superalloys. Gamma prime phases have an ordered crystalline lattice, which aids in providing added strength to the material. In addition, single crystal solidification techniques have been developed for superalloys that enable grain boundaries to be entirely eliminated from a casting, as well as increase the volume fraction of the γ′ precipitates. Alternatively, superalloys may be directionally solidified so as to include only longitudinally directed grains for added strength.
Oxide dispersion strengthened (ODS) alloys are also attractive for high temperature use because of their high temperature strength and oxidation resistance. However, such alloys have found limited application in practice because of the difficulties in manufacture including limited formability (especially of complex shapes), limited machinability, weldability, fabricability or repairability. The potential application of such alloys as a layer or coating is even more challenging due to problems with insufficient bonding of ODS materials to substrates.